In recent years a high-production method has been developed for plant germination in large truck farms and large nursery operations for plant germination followed by automatic transplanting of the seedlings: sheet material made from nonwoven fabric or paper is cut into strips and formed into a sleeve with overlapping longitudinal edges. The sleeve is filled by means of a proportioning apparatus with mixtures of peat, humus, sawdust and other aids commonly used in agriculture. These fillings, which vary greatly according to the type of plant and method of cultivation, will be referred to hereinafter as "substrates."
After the filling operation, the overlapping longitudinal edges are glued with a dispersion adhesive on a runner heated to 350.degree. to 400.degree. C. to form a tube. With a shearing device, sections 40 to 130 mm long are severed from the horizontally lying tube, the substrate is seeded and covered with chips of substrate or wood to retard drying. Conventional tubes have a diameter of 15 to 30 mm.
The seeded tube sections or cartridges are then placed into containers called flats, and cultivated in greenhouses for up to about 2 months, depending on the type of plant. During this germination phase the roots penetrate the sleeve material. Then the seedling are transplanted or shipped.
The sleeve material is strong enough for the transplanting operation; afterward it rots away so as not to interfere with further growth.
The use of such substrate tubes permits high production rates of as many as 1000 tube sections per minute.
Also, this method of germination saves time and substrate in comparison with conventional methods, and provides a cost advantage over manual methods. The smaller space which the tube sections occupy permits a high productivity per unit area, and lighter shipping weight and bulk are achieved. The uniform and stable substrate cartridges allow their easy removal from the germination flats, thus permitting automated transplanting. At the same time, gentle handling of the plants and root balls is assured. In a free-standing pot, very good formation of the seedlings is achieved.
One special advantage of this method of planting resides in the possibility of producing sleeves filled with substrate but unseeded for stock and then seeding them as needed. This offers the operator a high degree of flexibility and efficient utilization of machinery.
The method described above calls for certain processing and cultivation requirements.
Processing requirements (packaging).
Sufficient stiffness, stability of shape and flexibility of the sleeve material are necessary for optimum formation of the sleeve. For easy and trouble-free machinery operation the material should be as thin as possible and smooth.
Cultivation requirements:
During the germination phase of 5 to 12 weeks the sleeve must be rot-proof, that is, sufficiently stable in a moist environment. After transplanting or shipment and transportation the sleeve material must rot rapidly without additional chemical treatment, so as not to interfere with further root development and plant growth. It must not produce any residues harmful to the plant.
The sleeve is to hold the roots together without, however, constituting an impenetrable barrier for the roots; that is, sufficient porosity and good wet strength are required of the material. The ability to retain moisture is important (high water absorbency). The common specific weights of sleeve materials consisting of paper or nonwovens amount to 15 to 50 g/m.sup.2.
To prevent fungal attack (mildew formation) the sleeve material must be treated with a fungicide. This treatment also prevents the premature decomposition of the sleeve when it has to be stored for long periods of time before actual use.
The known sleeves have the following disadvantages:
The gluing of the sleeve with dispersion adhesives on the heated runner requires a short-term heat stability up to 40020 C. In the case of seaming of thermoplastic sheet material without a dispersion adhesive, the seam must be tight and long-lasting.
These requirements are only partially satisfied by the known sleeves, since thermal decomposition of the plastic compositions leads to brown or black seams, and the material thus degraded does not produce reliable seams.
The fungicidal preparations heretofore used made it unnecessary to add them to the sprinkling water, but they have proved to be unstable during the heating of the seams, so that the entire seam area became subject to fungus attack.
The sleeve materials heretofore used were mainly cigarette papers which have too little wet strength. Teabag papers and coffee filters have insufficient life, that is, their decomposition in the moist substrate by humic acid, bacteria and fungi takes place very quickly. Nonwovens of primarily polyester or polypropylene fibers produce only insufficiently tight seams when the sleeve is made with dispersion adhesives.
Fiber casing papers made of cellulosic fibers which are bonded with wet-strengthening agents are already in use in the vegetable sector. They withstand the short germination phases common in that sector, but they fail due to marked decomposition within 5 to 8 weeks. Production of such substrate cartridges for stock is not possible.
Another difficulty with the use of such cartridges is encountered in the addition of fertilizer. During the germination phase a slow-release fertilizing environment must be provided. The addition of a slow-release fertilizer with the sprinkling water is impossible under controlled conditions because of poor solubility; a uniform sprinkling mixture cannot be prepared. The addition of a slow-release fertilizer to the substrate is also very problematical on account of the great difference in specific weight between substrate and fertilizer. Homogeneous substrate mixtures cannot be produced (peat is specifically lighter).